Billie Eilish, born Billie Eilish Pirate Baird O’Connell, is using her voice as currency — and has plenty to spend on the world’s richest man, Elon Musk.

Pop superstar Billie Eilish ignited social media this week with a blistering critique of Elon Musk, labeling him a “f***ing pathetic p***y b**** coward” in a nearly unfiltered Instagram Stories post.

The 23-year-old first uploaded slides from the “My Voice, My Choice” account about what Musk could do with his wealth should he become the world’s first trillionaire, which the account claimed include...